#include "ThreadPool.h"

ThreadPool::ThreadPool(size_t threads) : stop(false)
{
    for (size_t i = 0; i < threads; ++i)
    {
        workers.emplace_back(
            [this]
            {
                while (true)
                {
                    std::function<void()> task;

                    {
                        std::unique_lock<std::mutex> lock(this->queue_mutex);
                        this->condition.wait(lock,
                                             [this]
                                             { return this->stop || !this->tasks.empty(); });

                        if (this->stop && this->tasks.empty())
                        {
                            return;
                        }
                        task = std::move(this->tasks.front());
                        this->tasks.pop();
                    }

                    task();
                }
            });
    }
}

ThreadPool::~ThreadPool()
{
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        stop = true;
    }
    condition.notify_all();

    for (std::thread &worker : workers)
    {
        worker.join();
    }
}

template <class F, class... Args>
auto ThreadPool::enqueue(F &&f, Args &&...args)
    -> std::future<typename std::result_of<F(Args...)>::type>
{

    using return_type = typename std::result_of<F(Args...)>::type;

    auto task = std::make_shared<std::packaged_task<return_type()>>(
        std::bind(std::forward<F>(f), std::forward<Args>(args)...));

    std::future<return_type> res = task->get_future();
    {
        std::unique_lock<std::mutex> lock(queue_mutex);

        // The lambda function captures 'shared_ptr<task>' by value
        // so that it stays alive until the task is executed
        tasks.emplace([task]()
                      { (*task)(); });
    }
    condition.notify_one();
    return res;
}
